1. Field of the Invention
The present invention relates to a new phosphine-borane compound and a method for producing the same. The new phosphine-borane compound of the present invention is useful as a raw material of an optically active phosphine ligand precursor frequently used as a raw material of the catalyst for an asymmetric synthesis reaction. The present invention also relates to a method for producing a hydrogen-phosphine-borane compound useful as an optically active phosphine ligand precursor.
2. Description of the Related Art
An organic synthesis reaction using a metal complex having an optically active phosphine ligand as a catalyst have been known for many years, and many results of research have been reported because it is very useful. Many optically active phosphine compounds of various structures have been developed in order to increase catalyst performance as described, for example, in “Asymmetric Synthesis in Organic Synthesis”, by Ryoji Noyori, John Willy & Sons, Inc., 1994, Canada (Review on optically active phosphine ligands) and “Catalytic Asymmetric Synthesis”, edited by Iwao Ojima, Wiley-VCH, Inc., 2000, Canada (Review on optically active phosphine ligands).
In recent years, a ligand which makes the phosphorus atom itself asymmetric has been developed and is reported to provide an excellent effect (for example, refer to Japanese Patent No. 2972887). In this case, an optically active phosphine ligand precursor is often supplied as a phosphine-borane in which an easily oxidized part is protected by a borane because the precursor is highly oxidizable and unstable. Many raw materials have been developed as a raw material of the precursor. Among others, a hydrogen-phosphine-borane having a P—H bond is one of the useful compound groups as a raw material of this precursor because the P anion works as a nucleophilic group and easily forms a P—C bond.
As a method for producing a hydrogen-phosphine-borane compound, there is mentioned a first method in which an alkyl (or aryl) dimethylphosphine-borane is allowed to react with butyllithium in the presence of (−)-sparteine at an ultra low temperature (−78° C.) to yield an asymmetric lithium methylene alkyl (or aryl) methylphosphine-borane, which is then oxidized by oxygen to yield an optically active alkyl (or aryl) methyl(hydroxymethyl)phosphine-borane, which is then oxidatively eliminated with potassium persulfate in the presence of ruthenium chloride (III) to produce an optically active hydrogen-phosphine-borane (for example, refer to Japanese Patent Laid-Open No. 2007-56007). Further, there is mentioned a second method in which a racemic hydrogen-phosphine-borane is allowed to couple with a chloroformate of an asymmetric alcohol to form a diastereomer, which is optically resolved by crystallization and then decomposed to produce an optically active hydrogen-phosphine-borane (for example, refer to Bull. Chem. Soc. Jpn., 75(6), (2002), 1359-1365).
However, a reversed type of stereoisomer cannot be obtained since natural (−)-sparteine is used in the first method using (−)-sparteine. Further, a compound showing properties equivalent to the reversed type of sparteine has been obtained by chemical synthesis through various difficulties in recent years. However, the compound is not easily available at present, and it is not regarded as an industrially useful means for obtaining a reversed type of stereoisomer (for example, refer to J.A.C.S, 128 (2006), 9336-9337). In addition, in the first method, the reaction requires a low temperature of −78° C., which requires a huge investment for reaction facilities. On the other hand, the second method using a chloroformate of an asymmetric alcohol is also based on the asymmetry of a natural alcohol in many cases. Therefore, it is often difficult to obtain a reversed type of stereoisomer.
Therefore, a development of a method has been desired which has high generality and allows production of any antipode without a special apparatus such as an ultra-low temperature cooling device when producing an optically active phosphine-borane compound.
Therefore, an object of the present invention is to provide an optically active phosphine-borane compound and a method for producing the same which are useful for the production of an optically active phosphine ligand frequently used as a raw material of the catalyst for an asymmetric synthesis reaction and allow easy production of any antipode.